This invention relates to power trains, as of earthmoving vehicles of the combined excavating-loading type, associated with auxiliary equipment such as hydraulic control circuits for the implement assemblies of the vehicles. More particularly, the invention is directed to a control system for the power train and auxiliary equipment of such a vehicle which are driven by a common prime mover, the control system being designed to enhance the operating efficiency of the vehicle. The invention is herein disclosed as adapted specifically for a loader, but with no unnecessary limitations thereto being intended.
The operations of a loader or like excavating-loading vehicle can be classified into the following three categories from the standpoint of the way the power developed by a prime mover such as an internal combustion engine is utilized; (1) propelling operation, wherein the engine power is used totally for propelling the vehicle; (2) combined propelling-excavating operation, wherein part of the engine power is used for propelling the vehicle and the remainder for actuating the bucket or like implement assembly of the vehicle; and (3) excavating operation, wherein the engine power is used totally for actuating the implement assembly.
The power trains of some excavating-loading vehicles incorporate a hydraulic torque converter the torque absorption characteristic of which can be varied, either continuously or stepwise, by the vehicle operator in accordance with the various operations of the vehicle classified above. The performance of such excavating-loading vehicles can be significantly enhanced if the torque converter is caused to have a relatively high torque absorption characteristic during its propelling operation, and a relatively low torque absorption characteristic during its propelling-excavating operation, as will be later explained in more detail with reference to FIG. 1 of the accompanying drawings. Such manual control of the torque absorption characteristic of the torque converter is objectionable, however, in that it adds to the labor of the operator.